The invention relates to the field of power supplies, and in particular to power supplies employing point-of-load (PoL) DC regulators receiving a DC PoL input voltage.
To maximize power conversion efficiency and availability, equipment such as telecommunication, data processing and networking equipment traditionally use an on-board 12V-bus power distribution architecture. Depending on system configuration, either a direct AC-to-12 VDC conversion or an AC-to-48 VDC power distribution followed by local, on-board, 48V-to-12V bus conversion may be used. Voltage regulation at the Point of Load (PoL), i.e. CPU, GPU, ASICs, memory and other system rails, is then realized with 12Vin non-isolated buck regulators configured for single-phase or multi-phase, interleaved, operation.
A recent trend in high performance computing and server boards is replacing the traditional 12V-bus with a 48V power distribution. Then, either a 2-stage conversion or a direct conversion from 48V to the Point-of-Load can be conveniently used to eliminate the intermediate 48V-to-12V bus conversion and power distribution losses typically associated with high current busses. Resulting efficiency gains in the range of 4%-5%, at the system level, from the AC source to the Point-of-Load, can be realized, and these can translate into lower operating costs for large installations like data centers or telecommunications central offices where a large number of voltage regulators are used.
48V-to-PoL regulators are nevertheless more expensive than legacy buck regulators, so it is important to maximize their efficiency to fully take advantage of this power distribution architecture. The high power rails, CPU, GPU, ASICs and memory, of a typical server motherboard are areas where increased conversion efficiency becomes more profitable. Industry organizations like the Open Compute Project (OCP) are setting standards intended to achieve a favorable balance between increased material costs and lower operating costs to minimize the total cost of ownership of the equipment. To that extent, certain minimum efficiency requirements are specified.
In many cases, applications with highly variable computing workloads may require high efficiency not only at the Thermal Design Power (TDP) point but also over a widely variable range of output currents, representative of the instantaneous CPU usage. It is common industry practice, in 12V-bus systems, to implement scalable output power by means of multiple, paralleled and interleaved non-isolated buck converters. This is a valuable feature that becomes more difficult to design in 48V-to-PoL systems, given the higher voltage conversion ratio and, consequently, the lower duty cycle that would be necessary for the standard buck topology. PoL regulators with isolated topology may be used, with benefits relating to input voltage polarity, duty cycle and load protection in case of hard failures, but they are subject to more stringent size constraints because they use more magnetic components as compared to 12Vin buck regulators and their corresponding 48Vin versions.
Another typical requirement for voltage regulators is to operate over a wide input voltage range. A nominal input voltage of +54.5 VDC can actually range from +40V to +59.5 VDC, and the extended minimum bus voltage may drop down to +38 VDC when the system is running off local battery backup voltage. Operation at low line is necessarily limited to short periods of time, with marginal impact on global operating costs, but the associated wide input voltage range imposed on voltage regulators may detract from the highest efficiency or maximum output power achievable from a given topology.
In summary, voltage regulator efficiency is affected by a number of design trade-offs and is therefore very difficult to maximize over a large set of operating conditions. While the multi-phase, interleaved buck converter is the industry workhorse for scalable output power, there is no similar, commonly accepted solution addressing scalability with respect to input voltage range currently available.